The invention relates to an electroweld fitting or an electroweld collar for pipes having a body of a thermoplastic and/or weldable material, particularly a polyolefin such as polyethylene, with a heating wire arranged adjacent an inner surface, preferably wound into a helical heating coil, to which current can be passed for welding.
West German published application DE-AS No. 28 23 455 discloses an electroweld collar of thermoplastic synthetic resin provided with a helical heating coil in the vicinity of its inner surface. In order to weld, the wires of the helical heating coil are connected with a source of current in order to conduct the requisite welding current to the helical heating coil. During welding, the surrounding material becomes plastic due to the heating of the helical heating coil.
To assure a good weld, a sufficient pressure between the surfaces to be joined must be maintained during the welding. This has hitherto been effected by forming the wall thickness of the synthetic resin body of the welding collar or welding fitting appropriately thick. Thereby it is achieved that, in accordance with the thermal gradients, the radially outer portions of the body are only warmed a little and remain substantially solid and rigid. The warmed plastic material in the interior in the vicinity of the helical heating coil thus cannot flow out. Because of the thus relatively large wall thickness of the weld fitting or weld collar, a large amount of material was required. Further, the weight and volume thereby became large, which was disadvantageous with regard to handling, transport costs, storage, etc.